The westernmost Late Miocene-Pliocene volcanic activity in the Vardar zone (North Macedonia)

Late Miocene to Pleistocene volcanism within the Vardar zone (North Macedonia) covers a large area, has a wide range in composition, and is largely connected to the tectonic evolution of the South Balkan extensional system, the northern part of the Aegean extensional regime. The onset of the scattered potassic to ultrapotassic volcanism south from the Scutari-Pec transverse zone occurred at ca. 8.0 Ma based on this study. Here, we focused on three volcanic centers located on deep structures or thrust faults along the western part of the Vardar zone, for which there is none to very little geochronological and geochemical data available. Pakosevo and Debriste localities are represented as small remnants of lava flows cropping out at the southern edge of Skopje basin and at the western edge of Tikves basin, respectively. Sumovit Greben center is considered as part of the Kozuf-Voras volcanic system, and it is located on its westernmost side, at the southern edge of Mariovo basin, which is largely composed of volcaniclastic sediments. We present new eruption ages applying the unspiked Cassignol-Gillot K-Ar technique on groundmass, as well as petrological and geochemical data, supplemented with Sr and Nd isotopes to complement and better understand the Neogene-Pleistocene volcanism in the region. Eruption ages on these rocks interlayered between sedimentary formations allow to better constrain the evolution of those sedimentary basins. Rocks from the three volcanic centers belong to the high-K calc-alkaline-shoshonitic series based on their elevated K content. The oldest center amongst these three localities, as well as other Late Miocene centers within the region, is the trachyandesitic Debriste, which formed at ca. 8.0 Ma, and exhibits the highest Nd and lowest Sr isotopic ratios (0.512441-0.512535 and 0.706759-0.706753, respectively). The basaltic trachyandesite Pakosevo center formed at ca. 3.8 Ma and its Nd and Sr isotopic ratios (0.512260 and 0.709593, respectively) bear the strongest signature of crustal contamination. The rhyolitic Sumovit Greben center is a composite volcanic structure formed at ca. 3.0-2.7 Ma. Its youngest eruption unit has a slightly higher Nd and lower Sr isotopic ratios (0.512382 and 0.709208, respectively) representing a magma with a lesser extent of crustal assimilation than the other samples from this center. The overall trend through time in the Sr and Nd isotopic ratios of the Late Miocene to Pleistocene mafic volcanic centers in the region implies an increasing rate of metasomatism of the lithospheric mantle.

Automated summary

Late Miocene to Pleistocene volcanic activity in the Vardar zone in North Macedonia is associated with the tectonic evolution of the South Balkan extensional system and the northern part of the Aegean extensional regime. The study focused on three volcanic centers with sparse geochronological and geochemical data, revealing that the onset of scattered potassic to ultrapotassic volcanism in the region occurred around 8.0 million years ago. This research provides insights into the evolution of sedimentary basins and the metasomatism of the lithospheric mantle over time.